Below is how to wipe android phone completely without app you can try.
Encrypt your device before you are getting ready to wipe it. It is important if the wipe doesn’t fully delete the data, a special key will be required to unscramble it.
To encrypt your android device, go to settings, security and select Encrypt phone.
How to wipe android phone completely without app by factory reset
Do a factory reset.
Go to Backup & Reset option in the settings menu and choose Factory data reset. Remember! This action will delete all the data on your phone, so you need to back up first.
Load dummy data.
You can load fake photos and contacts on your device. Don’t ask! We will explain later.
Perform another factory reset.
Perform another factory reset to erase the dummy content you loaded onto the device. This will make it harder for someone to locate your data because it buried below the dummy content.